The present invention relates to improvements in fluid cracking catalysts (FCC catalysts) containing a component obtained by synthesizing high contents of zeolite Y in situ within macropores of preformed silica-alumina microspheres composed of two different types of calcined reactive kaolin clay, and preferably blending the high zeolite content microspheres with functional additives, such as activity adjusting microspheres, as described in U.S. Pat. No. 4,493,902. One of the calcined clays is metakaolin. The other calcined clay is obtained by calcining kaolin clay through its characteristic exotherm (which typically occurs at about 1830.degree. F.). The microspheres are reacted with an alkaline sodium silicate solution that provides sodium and some of the silica utilized in the synthesis. In particular, the invention provides an economically attractive means for manufacturing the high zeolite content microspherical product, and utilizes coarse particle size ra (hydrated) kaolin to make microspheres of enhanced porosity. After spray drying, a portion of the spray dried microspheres is calcined to convert the clay to metakaolin and another portion of the same or similar microspheres of enhanced porosity is calcined under more severe conditions to cause clay in the microspheres to pass through the exotherm. A physical mixture of the two types of porous microspheres is employed in the synthesis of zeolite Y.
The following are illustrative of patents that disclose the use of kaolin calcined through the exotherm, alone or preferably in combination with metakaolin, in zeolite Y synthesis, including in situ zeolite Y synthesis by reaction of microspheres or other preformed particles composed of calcined clay. In some of the patents, the two different forms of calcined clay are in the same microspheres. In others the two forms of calcined clay are present in different particles as a physical mixture. Generally, these processes, which utilize sodium hydroxide as the sole source of sodium, feature a relatively low temperature aging step followed by a high temperature crystallization step, resulting in relatively low levels, e.g., 20-30%, of sodium zeolite Y. In some of the patents FCC catalysts are produced by providing the kaolin calcined to undergo the exotherm in the form of spray dried microspheres and utilizing metakaolin either in the form of separate microspheres or in the form of powder.
U.S. Pat. No. 3,367,886 PA1 U.S. Pat. No. 3,367,887 PA1 U.S. Pat. No. 3,506,594 PA1 U.S. Pat. No. 3,647,718 PA1 U.S. Pat. No. 3,657,154 PA1 U.S. Pat. No. 3,663,165 PA1 U.S. Pat. No. 3,932,268 PA1 a. 2988.5 g of a sodium aluminate solution having a nominal composition of 6% Al.sub.2 O.sub.3, 19% Na.sub.2 O, and the balance water. PA1 b. 392.1 g of NaOH pellets PA1 c. 1361.3 g DI (deionized) water PA1 a. 6593.2 g of N.RTM.Brand sodium silicate solution having a nominal composition of 8.7% Na.sub.2 O and 29% SiO.sub.2. PA1 b. 509.8 g of NaOH pellets PA1 c. 2084.9 g DI water PA1 a. 6593.2 g of N-Brand sodium silicate solution having a nominal composition of 8.7% Na.sub.2 O and 29% SiO.sub.2. PA1 b. 509.8 g of NaOH pellets PA1 a. Sodium aluminate solution (#1 above) 97 cc/min PA1 b. Sodium disilicate solution (#2 above) 160 cc/min
U.S. Pat. No. 4,235,753 discloses a process for crystallizing zeolite Y in microspheres composed of metakaolin and separate microspheres composed of kaolin calcined through the exotherm by hydrothermal reaction with sodium hydroxide solution in the presence of seeds. Illustrative examples indicate that the crystallized products contained a maximum of 30% zeolite although the patent mentions crystallized products containing 2 to 75%, and most preferably 10-50% zeolite.
U.K. Nos. 1,271,450 and 1,342,977 (e.g., EXAMPLES 2 and 4 of the latter) illustrate the preparation of cracking catalyst particles containing synthetic faujasite (zeolite X or Y) by spray drying an aqueous slurry of raw (uncalcined) kaolin, calcining the spray dried particles at 1300.degree. F. (or at 1000.degree. F. and then at 1300.degree. F.) to convert the kaolin in the microspheres to metakaolin, mixing the particles with a sodium silicate-sodium hydroxide solution, adding sodium aluminosilicate seeds and refluxing to crystallize the zeolite. Similarly, U.S. Pat. No. 3,377,006 teaches the preparation of high purity zeolite Y by reaction of finely divided metakaolin with sodium silicate in the presence of seeds. Kaolin calcined through the exotherm is not utilized in practice of these processes. Kaolin calcined to undergo the exotherm is a desirable source of reactive silica in the synthesis of Y faujasite because it results in a unique crystallization residue of calcined clay that somehow contributes significantly to the thermal stability and metals tolerance of the zeolitic component. Thus, my experience is that catalysts prepared by reacting microspheres containing only the metakaolin form of calcined kaolin clay with a seeded sodium silicate solution have not resulted in thermally stable, metals tolerant catalysts.
U.S. Pat. No. 4,493,902, the teaching of which are incorporated herein by cross-reference, discloses novel fluid cracking catalysts comprising attrition-resistant, high zeolite content, catalytically active microspheres containing more than about 40%, preferably 50-70% by weight Y faujasite, and methods for making such catalysts by crystallizing more than about 40% sodium Y zeolite in porous microspheres composed of a mixture of two different forms of chemically reactive calcined clay, namely, metakaolin and kaolin clay calcined to undergo the characteristic kaolin exothermic reaction, sometimes referred to as the spinel form of calcined kaolin.
In practice of the '902 technology, the porous microspheres in which the zeolite is crystallized are preferably prepared by forming an aqueous slurry of powdered raw (hydrated) kaolin clay (Al.sub.2 O.sub.3 :2SiO.sub.2 :2H.sub.2 O) and powdered calcined kaolin clay that has undergone the exotherm together with a minor amount of sodium silicate which acts as fluidizing agent for the slurry that is charged to a spray dryer to form microspheres and then functions to provide physical integrity to the components of the spray dried microspheres. See example 1. The hydrous clay, exemplified by ASP.RTM. 600 kaolin has a particle size distribution such that about 80% by weight is finer than 2 microns as determined by aqueous sedimentation. The spray dried microspheres, each containing a mixture of hydrated kaolin clay and kaolin calcined to undergo the exotherm, are then calcined under controlled conditions, less severe than those required to cause kaolin to undergo the exotherm, in order to dehydrate the hydrated kaolin clay portion of the microspheres and to effect its conversion into metakaolin, thus resulting in microspheres containing the desired mixture of metakaolin, kaolin calcined to undergo the exotherm and sodium silicate binder. The '902 patent teaches (col. 8) that the proportions of hydrated and precalcined clay used to form the microspheres are such that the calcined microspheres comprise about 30-60% by weight metakaolin and about 40-70% by weight kaolin characterized through its characteristic exotherm. In illustrative examples of the preferred embodiment of the '902 patent, about equal weights of hydrated clay and spinel are present in the spray dryer feed, whereby the resulting microspheres after calcination contain somewhat more clay that has undergone the exotherm than metakaolin because of the loss of weight of the hydrated kaolin precursor during its conversion to metakaolin.
Another method described in the '902 patent at column 6, involves spray drying a slurry containing a mixture of kaolin clay previously calcined to metakaolin condition and kaolin calcined to undergo the exotherm but without including any hydrated kaolin in the slurry, thus providing microspheres containing both metakaolin and kaolin calcined to undergo the exotherm directly, without calcining to convert hydrated kaolin to metakaolin. However, the patent teaches that less attrition resistant zeolitized microspheres are produced by this approach. Still another method described in Example 6 involves spray drying a 60% solids deflocculated slurry hydrated kaolin clay believed to be HT kaolin as described in Example 1 of U.S. Pat. No. 3,663,165 to form microspheres part of which are calcined under conditions to convert them into metakaolin and another part of which are calcined to undergo the exotherm. As described in the cross-referenced '165 patent HT clay is "a fine size fraction of hydrated Georgia kaolin clay, corresponding to a No. 2 paper coating grade." Thus, HT clay is similar to ASP.RTM. 600 clay which has the same particle size distribution, corresponding to that of No. 2 paper coating grade. A relatively low level of zeolite Y (44%) was reported in Example 5 and the crystallization of 50% or more zeolite Y achieved by the preferred technique of using a mixed hydrous/calcined clay spray dryer feed was not achieved.
In carrying out the various embodiments of the invention described in the '902 patent, the microspheres composed of kaolin calcined to undergo the exotherm and metakaolin or the physical mixtures of microspheres are reacted with a caustic enriched sodium silicate solution in the presence of a crystallization initiator (seeds) to convert silica and alumina in the microspheres into synthetic sodium faujasite (zeolite Y). The microspheres are separated from the sodium silicate mother liquor, ion-exchanged with rare earth, ammonium ions or both to form rare earth or various known stabilized forms of catalysts. The technology of the '902 patent, especially the preferred embodiments, provides means for achieving a desirable and unique combination of high zeolite content associated with high activity, good selectivity and thermal stability, as well as hardness (attrition-resistance). By appropriate ion-exchange treatment, desirable cracking selectivity is achievable.
EPA No. 0,194,101, published Sept. 10, 1986 which claims priority from U.S. Ser. Nos. 707,635 707,362, and 750,813, all now abandoned, describes variations of the ion-exchange treatment applied to the sodium form high zeolite content microspheres of the '902 patent to provide so-called "octane" catalysts, the zeolite component of which is characterized by having a low sodium content, reduced unit cell size and the absence of rare earth or the permissible presence of minimal amounts of rare earth. These known variations of zeolite Y faujasite are frequently referred to as stabilized and/or ultrastabilized zeolite Y. Hereinafter the various stabilized forms of zeolite Y, e.g., calcined H-Y, Re-Y, will be called ultrastabilized Y which now has a broader meaning than the original term which was limited to zeolite Y having unit cell size below 24.45 Angstrom units.
Technology described in the '902 patent has met widespread commercial success. Because of the availability of high zeolite content microspheres which are also attrition-resistant, custom designed blended catalysts are now available to oil refineries with specific performance goals, such as improved activity and/or selectivity without incurring costly mechanical redesigns. A significant portion of the FCC catalysts presently supplied to domestic and foreign oil refiners is based on the technology.
As mentioned, the preferred technique for making microspheres used in practice of the '902 technology utilizes the composite microsphere approach (microspheres containing both metakaolin and kaolin calcined to undergo the exotherm), substantially as described in the '902 patent, e.g., Example 1, in which microspheres are prepared by spray drying a slurry of mixture of clay previously calcined to undergo the exotherm, e.g., SATINTONE.RTM. calcined clay, and about an equal weight of hydrated fine particle size kaolin, e.g., ASP.RTM. 600 clay. The resulting spray dried microspheres are calcined to convert the hydrated kaolin component of the microspheres to metakaolin and are then employed as the host for zeolite synthesis. One drawback to the preferred process, from the production point of view, is that about half the clay, e.g., SATINTONE.RTM. clay, is calcined twice. Calcination is an energy consuming process. Another drawback is that the hydrated kaolin, e.g., ASP.RTM. 600 clay, is a high quality, relatively expensive form of kaolin, prepared by removing a substantial amount of large (plus 2 microns) clay particles from a crude clay and resulting in a lower value coarse particle size kaolin by-product stream.
In view of the commercial importance of FCC catalyst blends based on high zeolite content microspheres derived from kaolin clay there has been a continuing search for means to produce high zeolite content microspheres more economically, without sacrifice in attrition-resistance, activity, selectivity, thermal stability and metals tolerance. This present invention is a result of these searches.